1. Field of the Invention
This invention relates generally to computer adapter cards, and more particularly to computer adapter cards that are capable of interconnecting data buses having target peripheral devices to a host computer system.
2. Description of the Related Art
As the power of applications, processors, and storage devices increase, high-end computer users are seeking ways to optimize their computer systems to achieve the highest level of performance. For example, most of today's computer systems are highly modular systems that enable them to be modified and equipped with just the right software and hardware. Typically, a computer's mother board includes several peripheral component interconnect (PCI) slots that are configured to receive adapter cards, such as SCSI adapter cards. These SCSI adapter cards act as a reliable and efficient interface between the host computer and any number of peripheral devices. In general, once a SCSI adapter card is inserted into the host computer's PCI slot, a SCSI bus (typically in the form of a ribbon cable) is used to interconnect one or more peripheral devices (also known as target devices) to the SCSI host adapter.
In recent years, there have been many improvements to the SCSI bus technology which has lead to the development of several different types of SCSI buses, each having their own performance characteristics. For ease of discussion, FIG. 1A is an example of an Ultra bus system 100, which is in the form of a cable 102 that includes several connectors 104. The Ultra bus system 100 typically has seven (7) connectors 104 which are 50 pin connectors, and the cable 102 is capable of communicating data at speeds up to about 20 Megabytes/second, for 8-bit devices. Alternatively, if the cable 102 is an Ultra Wide bus, the Ultra bus system 100 will be capable of communicating data at speeds up to about 40 Megabytes/second, for 16-bit devices. Also, Ultra Wide buses typically have fifteen (15) connectors 104 having 68 pins. Accordingly, the Ultra bus system 100 is capable of interconnecting either up to 7 or up to 15 target devices 106, in a parallel arrangement, to the SCSI host adapter. Thus, depending on whether the Ultra bus system 100 has an Ultra or Ultra Wide bus, it will be capable of supporting data transfer rates up to 20 or 40 Megabytes/second.
FIG. 1B illustrates an Ultra2 bus system 120 having a low voltage differential (LVD) cable 122 and respective 68 pin connectors 124. In general, the LVD cable 122 of the Ultra2 bus system 120 is known to be a lower power consuming system than the Ultra bus system 100, and provides the ability to drive cable lengths up to 12 meters or more. This is substantial when compared to the Ultra bus system 100, which can only typically drive cable lengths of about 3 meters. Most significantly, the Ultra2 bus system 120 is capable of running at data transmission speeds up to about 80 Megabytes/second, for 16-bit Ultra2 devices. As can be appreciated, higher performance systems will typically want to take advantage of the high data transmission speeds by incorporating Ultra2 bus systems 120 into there computer system. To fully take advantage of the increased data transmission speeds offered by the Ultra2 bus system 120, Ultra2 target devices 126 should be connected to the connectors 124. Unfortunately, when older Ultra target devices 106 are connected to the Ultra2 bus system 120, the transmission speeds for all other devices on the bus, including the Ultra2 target device 126, will suffer a substantial reduction in speed, which is typically about half or more.
For example, assume that the Ultra2 target device 126 was enjoying a transmission rate of about 80 Megabytes/second along the Ultra2 bus system 120 before the Ultra target device 106 was connected to the bus. After the Ultra target device 106 is connected to the bus, the transmission rate for all target devices (Ultra2 and non-Ultra2 devices) connected to the bus will not be more than the transmission rate of the Ultra target device 106. Therefore, if the Ultra target device 106 is an Ultra Wide device that is capable of running at 40 Megabytes/second, then the fastest the Ultra2 target device 126 can run is 40 Megabytes/second. This is true even though both the LVD cable 122 and the Ultra2 target device 126 is capable of running at speeds up to about 80 Megabytes/second.
Accordingly, if a user desires to install an LVD cable 122 to interconnect the SCSI host adapter to peripheral devices, such as, hard drives, CD-ROMs, DVD drives, tape drives, and the like, the user will also have to replace all non-Ultra2 peripheral devices to take advantage of the higher speeds offered by an Ultra2 bus system. As can be appreciated, the replacement of all peripheral devices can be a costly solution, considering that only selected speed sensitive peripheral devices need to run at the Ultra2 speeds. Furthermore, being that SCSI Ultra bus is a more established technology, there is a greater likelihood that a majority of the peripheral devices that are currently installed in existing computer systems will be Ultra target devices. As such, many users that desire the improved data transmission speeds of Ultra2 target devices will decide not to install an Ultra2 bus and an Ultra2 peripheral device because, if older Ultra target devices are connected to the Ultra2 bus, the faster transmission rates of the SCSI Ultra2 will not be realized.
In view of the foregoing, there is a need for a SCSI technology adapter that enables use of both Ultra and Ultra2 target devices without reducing the data transmission rates of the faster Ultra2 target devices.